1. Field of The Invention
The present invention relates to the mating contacts used in electrical connectors and, more particularly, to a low insertion force, high contact normal force, mating male and female electrical contact structure.
2. The Prior Art
Metal pins have been used in the electrical connector industry for making electrical contact between a plug connector and a receptacle connector. Various single and dual spring arm female contact electrical terminals have been provided in the past for making electrical contact with male terminals such as pins, blades, edge card contact pads and the like. In order to establish satisfactory electrical connection, one of the terminals must exert sufficient pressure on the other resulting in a minimum contact normal force being exerted when the terminals are in a final mated position. However, this pressure causes frictional drag during insertion and removal, therefore, the male terminal must be inserted into the female terminal with sufficient force to overcome the resistance to insertion presented by the female terminal. In addition, the insertion force of the contact structure must include a lifting component which represents the force required to lift or spread the female contact portions apart to permit insertion of the male terminal into the female terminal as well as the horizontal frictional component which is a result of the female contact portions wiping against the meal terminal during the insertion As a result, in multi-circuit arrangements including a large number of female terminals mounted in a connector adapted to mate with a male connector having a correspondingly large number of male terminals, the individual insertion forces associated with each pair of terminals combine so that the overall insertion force required to mate the male and female connectors may be extremely large.
Earlier efforts to provide an electrical contact structure characterized by reduced insertion force have generally included modifying the female terminal or contacts. In U.S. Pat. No. 4,175,821, for example, a female terminal is disclosed which includes a dual opposed spring arm contact member wherein the contact portions of the opposed arms are axially offset from one another in the longitudinal direction. As a male pin contact is inserted between the female spring arms, the male pin engages the first spring arm on the female terminal and lifts it out of the way, before contacting the second spring arm and moving that contact of the way. AS a result, a lower peak insertion force is achieved because the male terminal lifts only one female spring arm at a time instead of two at a time. The design of this patent has several shortcomings. For example, the female terminal is adapted to receive a conventional square pin male terminal which includes a relatively short, chamfered tip portions. The tip portion of the male terminal typically is a rough machined surface which wipes against the precious metal plated contact portion on the female terminal. Repeated mating results in abraded contacts which tends to make the contact arrangement electrically unreliable in prolonged use. Increasing the precious metal plating in the contact area results in increased cost which is undesirable.
Another modified low insertion force female terminal is disclosed in U.S. Pat. No. 4,607,907 at their free ends. The female contact in this patent is a stamped and formed terminal which includes a rearward box-like member from which extend cantilevered spring arms having contact portions at their free ends. The contact portions are axially longitudinally offset similar to the contact portions in the aforementioned patent, but, in addition, they are configured so that they overshoot the midline of the insertion region which permits lower spring rates to be used. The female contact further includes horizontal spacing between the cantilevered spring arms so that the contact portions are horizontally spaced one from the other. This permits the contact portions to be plated with precious metals in a lower cost process. This female contact provides a lower peak insertion force for the same reasons, i.e. the male lifts one cantilevered spring arm at a time during insertion. The overshot design of the contact portions permits lower spring rates in the spring members to be used, so that the stiffness of each spring member is reduced and the force required to lift each spring arm contact during pin insertion is reduced.
This design also possesses several shortcomings. As with the first mentioned female terminal, the rough cut abrasive edge of the chamfered lead-in on the male pin scrapes against the precious metal coated contact portions of the spring arms during pin insertion. Long term electrical reliability in repeated mating operations is generally not obtained. The female terminal is stamped and then formed in a manner which produces a significantly large amount of wasted sheet metal stock. Furthermore, because these female terminals are formed after stamping to provide the box portion and opposed spring arm structure, they cannot be provided on a carrier strip spaced apart by centerline spacingly adapted for ready insertion in a connector housing in a single stamping operation. Instead, after they are formed, they must be repositioned to a spacing appropriate for insertion into a housing. This requires additional manufacturing and assembly steps in use.
Also another low insertion force mating contact structure is disclosed in U.S. Patent No. 4,740,180 having a male terminal and a female terminal. The male terminal is an elongate conductor having at least one surface extending the length thereof and including a final contact portion joining a forwardly extending lead-in portion which has a gradual twisted cross-section relative to the final contact portion. The female terminal includes at least one spring arm with a contact portion adapted to electrically engage the surface of the male terminal. The spring contact portion slidingly engages the surface in the lead-in portion being effective to increasingly deflect the contact portion of the spring arm as the male terminal is inserted from initial position to a final position when the female contact portion is on the final contact position of the male terminal. The normal force between the contact portion of the spring arm on the surface of the male terminal gradually increases as the male terminal is inserted into the female terminal until a final mated position is achieved.
This mating contact structure works well for large size connector which allows the insertion length to be long enough for separating the contact terminal into a lead-in twisted portion and a final contact portion, yet it does not meet the compact size requirement, wherein the contact terminal length is limited for meeting the compact size trend in the connector industry.
Further another low insertion force male contact is disclosed in U.S. Pat. No. 5,290,181 at its laterally offset, symmetrical diverging beams. This split male contact although can reduce insertion force due to the flexibility of the split beams, it is apt to deform permanently at its split beams. In other words, the split beams are apt to loose their flexibility after long term use. This kind of male contact will have larger and larger insertion force with respect to a complementary female contact after repeated insertion/withdrawal therewith.
It is requisite to provide a new male contact to solve the above problems.